SAN DIEGO -- A trailer burst into flames Monday at the scene of the apparent arson fire that leveled a five-story condominium building under construction in University City last week, 10News reported.

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The metal storage shed at the blackened site east of University Towne Centre mall was reported on fire about 6:30 p.m., according to the San Diego Fire Department.

It took engine crews about 20 minutes to extinguish flames. The cause of the blaze is under investigation.

Last week's pre-dawn, three-alarm blaze caused in excess of $20 million in property losses, officials said.

Initial evidence suggested that the inferno off La Jolla Village Drive may have been an act of eco-terrorism carried out by affiliates of a militant anti-development group, the Earth Liberation Front.